How do I do this?

I've had another (untested) thought on this that I think should work OK for some jobs and should be pretty straightforward to do on a vertical mill.

You could tweak the arrangement shown by offsetting the D piece a bit further away from the bore than in the pictures, so that it's more fully held around the circumference and able to be held by friction fit.

Martin.

Martin,

That looks very promising.

MichaelG.

Now, getting a bit more sophisticated, imagine that the extra part hole in the last picture is machined on a slight angle, and the orange key piece has its flat on the same angle. Now you have a tapered key which will wedge in.

I dunno how you would get it out....maybe a tapped hole on the outside face

John

A similar idea to the half round hole and insert would be to broach (or cut a slot) a rectangular hole and use a rectangular key.

Paul.

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Paul,

Would there be any benefit ? ... I think not, but would be pleased to see your reasoning.

A rectangular hole is [typically] harder to produce, and introduces 'stress raising' corners just where we don't want them.

MichaelG.

Hi Michael,

Making a square slot in the side of a hole is very easy with a keyway broach, simply by pressing it thru the hole. The difference with this application is that the shaft does not have a slot. And yes, the square corners are stress raisers but rectangular or square keys are used on millions of pulleys and is the normal way to attach it to a shaft.

You have stated that the pulley is subjected to high torque which suggests that it should have a proper keyway and key and should be firmly secured to the shaft by using clamping screws or press fitting the pulley to the shaft. The shaft should be removed from the motor if you intend to use a press fit otherwise you may damage the bearings.

Paul.

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Paul,

For the avoidance of any future confusion:

No I have not ... all I have done is comment upon Martin's excellent suggestion.

MichaelG.

Paul, the D shaped hole is in the end of a bar so a blind hole, can't push a broach through it. This is not the boss of teh pully but the end of a moror shaft.

If it could be broached then you would just make a D shaped broach and not faff about with loose keys.

Blowlamps earlier sketch does use a "square" key except the corners are rounded to suit the cutter having to be used from the end.

Edited By JasonB on 03/03/2015 12:32:59

Hi Jason (and all others), there have been a lot of good suggestions offered but I think that we have all gotten a little side tracked with clever designs instead of looking at the real problem.

The original question was how to make a "D" shaped hole. and later Thomas said :-

" Yes, this is to go on an existing electric motor with this shape already on the end of it's shaft - it is also too short to cut a keyway or any other hole in it as the motor would foul onto the chuck.

I could do a simple grub screw job but the mechanism it is powering will be under a lot of resistive torque (is that a term??). In other words the motor shaft needs to have a really good grip on the arbor that requires this odd hole, otherwise it may fail and I am unsure if a grub screw is up to the job. "

This sounds like a standard motor and pulley arrangement (Thomas please confirm) which normally uses a grub screw to lock the pulley to the shaft.

My lathe has a similar arrangement with a 1kw motor with a 16mm shaft and a flat on the shaft. An aluminium vee belt pulley is only secured by an M8 grub screw. The torque from small (1440 rpm) motors is not that great and a grub screw is all that is needed. The secondary shaft and pulleys run at a much slower speed and much higher torque, therefore it is fitted with a key plus a screw to clamp it in position.

Paul.

It occurs to me that one could cut that exact profile on a lathe albeit it would be a tedious excercise in patience. I sometimes forget that one can hand turn the chuck through the arc required and use the slide for the flat. the tool grind would be interesting. A centra hole would releive pressure and allow the eventual manual undercuts.. equally tedious.